The present invention relates to air vent valves to relieve a vacuum developed in conduits. More particularly, it refers to a dual ball valve for vacuum relief of domestic sewage piping systems in residential, commercial, industrial and institutional buildings.
A single ball valve air vent is described in U.S. Pat. No. 6,234,198. Such a valve has received widespread commercial acceptance and is adequate to carry out its intended purpose. However, for large sewer pipes with drainage from multiple commodes a single air flow channel may not be adequate. For this reason the search continues for more efficient air flow in air vent valves.